In the past, light-emitting diodes (LED)s were substantially more expensive than alternative technologies such as cold cathode fluorescent lamp (CCFL) backlighting. However, modern mass production and advances in manufacturing have made LEDs much less expensive. Given their lack of toxic components in contrast to the mercury used in CCFL as well as their increased efficiency, LED backlighting is thus rapidly replacing older technologies such as CCFL. One issue that remains with regard to the adoption of LED technology is LED flicker.
In particular, flicker may occur in systems that use pulse width modulation (PWM) to control the LED dimming (relative brightness). In contrast, a constant current reduction dimming approach would instead change the amount of current driven into an LED string. But such a change in current level results in a change of the color temperature and also tends to produce a non-linear change in luminosity. In contrast, PWM dimming keeps the color temperature substantially constant and results in a linear dimming profile. PWM dimming control is thus a popular alternative to a constant current reduction approach. But the resulting flicker in PWM-dimmed systems may discourage a consumer's adoption of LED technology. This is detrimental to the environment given the increased greenhouse gas emissions associated with the relatively-poor efficiency of alternative lighting technologies and their associated toxic waste.
Accordingly, there is a need in the art for improved LED PWM dimming methods and systems that eliminate flicker.